visible light communication


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Visible Light communication Sustainable Energy-Efficient Wireless Application Using Light 2

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INTRODUCTION Lighting is a major source of electric energy consumption. Visible light communication is a data communication medium using visible light between 400 THz-800THz. General characteristics: Visibility Security Harmless for human body Unregulated Using in restricted area Eye safety 4

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MOTIVATION Now, researchers came to realize that WLED devices could also be used for wireless purposes. LEDs rends to be considerable cheaper than RF. Optical wireless allows easy bandwidth reuse and improve security. It doesn’t generate RF contaminations. Replacing RF device will reduce interference in RF band. RF radiation in hospital and airplane will be vanished . Large amount of energy can be saved. 5

Technology (1/3):

Technology (1/3) Every kind of light source could be used as sender. LEDs are the predominant choice for transmitters They can be switched on and off in very short intervals. Receivers Photodiode receivers. CCD and CMOS sensors. 6

Technology (2/3):

Technology (2/3) Schematic view of the entire process of transmitting and receiving data. Data Light source Modulation (PPM/FSK) Data Demodulation (PPM/FSK) PD or CCD 7

Technology (3/3):

Technology (3/3) Phosphorus LEDs can achieve up to 40 Mbps. By using RGB LEDs data rates can go up to 100 Mbps. RCLEDs (resonant cavity LEDs) can achieve data rates up to 500 Mbps. RCLEDS use reflectors (which serve as mirrors) to enhance the emitted light They also have increased spectral purity when compared to conventional LEDs which further improves communication capabilities LEDs are energy-efficient and are becoming increasingly inexpensive. 8

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Why WLED ? Brightness / Power ratio Cost / Brightness ratio Incandescent Lamp Halogen Lamp Fluorescent Lamp LED LED LED LED 2003 2005 2010 2015 50 100 150 0 1 10 100 9

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VLC Characteristic Data rate (bps ) 115K 4M 100M 480M 16M 50M UFIR FIR IR VI VLC 1 11 3 Distance (m) 2 6 20 50 UWB 802.11a 802.11b Bluetooth ZigBee 10

Data transmission:

Data transmission Modulation (with respect to VLC) is used to transform the data (given as a sequence of 0s and 1s) into a series of light pulses Two main alternative modulation schemes:  sub -carrier pulse position modulation (SC- kPPM ): - data is separated into groups of log k bits each and there is only a single pulse for each group  frequency shift keying (FSK): - signal frequency determines whether or not the currently transferred bit is 0 or 1 11

Sub-carrier pulse position modulation :

Sub -carrier pulse position modulation Data is separated into blocks of log k bits. K possibilities for each block. Transmission time of a single pulse determines which of the k possibilities is represented by the current block 12

Frequency shift keying:

Frequency shift keying Two distinct values (0 and 1) are represented by two distinct pulse frequencies. This (simple) form of FSK is also referred to as binary FSK. 13

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Transmitter/receiver of VLC Visible light LED Fluorescent lamp PIN photo diode Avalanche photo diode 14

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VLC vs. RF Characteristics Property VLC RF Visibility Yes No Bandwidth Unlimited, 400nm~700nm Regulatory, BW Limited EMI No High Hazard No Yes Power Consumption Relative low Medium Coverage Distance Short Medium 15

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Applications Under water communication system Inside airplane communication 16

4. Traffic light-car communication:

Applications 3. Vehicle to vehicle messaging 4. Traffic light-car communication 17

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Indoor broadcasting system. Applications 18

VLC System:

VLC System 19

Indoor Broadband:

Indoor Broadband 20

Feasibility at 4 Mb/s – PC-PC visible link:

Feasibility at 4 Mb/s – PC-PC visible link 21

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Advantages Transmit data by sockets of existing light fixtures. Alleviate a number of problems associated with the radio frequency (RF) communication systems. consume far less energy . Security. Harmless for human body. Eye safety. 22

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Disadvantages Atmospheric absorption Shadowing Beam dispersion Interference from background light sources 23

Providing an uplink:

Providing an uplink VLC is a natural broadcast medium Sending back information to the source is sometimes desired There are three major approaches to providing an uplink to the camera. Co-locating the light source with a VLC receiver - Advantage: data can be sent back - Drawback: sending light back is costly (energy-wise) Using a retro-reflector to return incident light - Advantage: data can be sent back from several sources in parallel - Drawback: uplink data rates are rather low using this approach Fitting the light source with a RF or IR receiver - Advantage: data can be sent back fast - Drawback: no VLC is used, all disadvantages of not using VLC (EM interference etc.) 24

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Conclusion There are many application that can be realized using Visible Light Communication. Optical Wireless Communications is an emerging technology that truly delivers data at very high rate with fibre-like quality 25

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Reference Visible_light_communication IEEE VLC tutorial ( ) The Case for Vehicular Visible Light Communication (VLC): Architecture, Services and Experiments By Cen Bi Liu 26

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Questions ? 27

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